Ionic liquids (ILs) are salts composed of distinct organic cation and anion pairs that melt at or below 100° C. Ionic liquids possess remarkable properties, which make them ideal candidates as alternative solvents for synthesis, catalysis and chemical separations (e.g. negligible vapor pressure, high thermal stability, large liquid range) see reference (1). Nitrogen based ILs such as imidazolium (1), ammonium (2) and pyridinium (3) salts are the most widely developed while few reports on sulfonium (4) or phosphonium ionic liquids (5) (PILs) are present in the literature despite their advantages, such as higher thermal stability and increased tolerance towards basic conditions.

The possible substituents at the cation is highly flexible and when paired with a wide range of potential anions, an extremely large pool of ionic liquids can be generated, all of which contain a variety of properties that can be tuned in order to target certain characteristics, such as melting point, polarity and viscosity to mention just a few. In addition to these more familiar applications, task-specific ionic liquids, containing unusual but potentially useful functionalities, impart these materials with attractive properties not observed in more conventional IL systems. For example, ammonium salts synthesized from natural amino acids (6) produce bio-degradable, chiral solvent media, see references (2-6). Catalytically active organometallic complexes can be tethered to ILs, such as the Grubbs Generation I/II catalysts (7), which are highly effective in ring closing olefin metathesis (RCM) with no evidence of catalyst leaching, see reference (7).

Recently, ionic liquids that contain highly fluorinated substituents appended to either the cation or anion have been reported and utilized as a non-volatile fluorous solvent alternative in fluorous biphasic catalysis (8a), see reference (8) as surfactants for other ionic liquids (8b), see reference (9) and in phase transfer catalysis (8c), see references (10, 11 and 12). Eventually, with intuitive creativity, the concept of structurally manipulating ILs evolved into a paradigm shift in this research field, as these salts are now not only viewed as alternative solvents, but also as novel functionalized materials (e.g. lunar telescope mirror, see reference (11), rewriteable imaging surfaces, see reference (12), lubricants see reference (13), biosensors, see reference (14)).
Ionic liquids have been widely used as solvents for a variety of catalytic methods since they display limited miscibility with organic solvents resulting in a system that allows for efficient catalyst recovery through simple phase separation techniques. However, considering the ionic media does not solubilize apolar organic reagents such as long chain hydrocarbons or neutral metal complexes easily, in some cases, this can result in a decrease in catalytic activity when compared to the traditional homogeneous methods. This limits the application of ionic liquids as solvents for catalysis. In order to improve the solubility of apolar substrates in ionic liquids, an increase in lipophilicity is required.
Introducing fluorinated substituents into the ionic liquid media is one approach to improve the lipophilicity. A further advantage of incorporating perfluorinated substituents is the possibility of generating fluorous biphasic systems (FBSs), see reference (15). This is a temperature dependent separation methodology where the fluorous phase, and an organic phase become miscible at elevated temperatures and then upon cooling, the fluorous and organic layers separate. This concept can be exploited in catalysis. In the two-phase system, a fluorous-tagged catalyst (containing perfluoroalkyl ligands) will selectively partition into the fluorous phase, while the organic substituents will be contained in the organic phase. By increasing the temperature, the system becomes homogenous and the catalysis will proceed. Upon completion of the reaction, the temperature is decreased which initiates phase separation, allowing for isolation of products in the organic layer and recovery of catalyst in the fluorous layer, which can then be recycled.
One drawback to this system is that fluorous solvents are extremely volatile, however, the benefits of homogenous reaction conditions in conjunction with effective product isolation and catalyst recovery are combined into one system. Furthermore, although fluorous solvents display interesting properties and valuable characteristics for many reactions, in some cases, the fluorinated solvent is not capable of forming monophasic solutions at elevated temperatures and therefore does not allow for the reaction to occur with reactants not soluble in the fluorous phase. Strategies to avoid these issues include the utilization of the combined effects of ionic polarity and fluorous properties to enhance selective solubility. This can be achieved by incorporating fluorinated phosphonium ionic liquids as phase transfer catalysts in heterogenous fluorous systems.
A fluorinated silylborate anion [B{C6H4—(SiMe2CH2CH2C6F13)-p}4] was paired with a 1-butyl-3-methylimidazolium cation [BMIm] (8a) to generate a solvent media capable of undergoing fluorous biphasic catalyst recycling, see reference (8). The fluorous ionic liquid was insoluble in water and soluble in polar organic solvents and some apolar solvents, in addition to being capable of solubilizing various alkenes and both the non-fluorinated and fluorinated Wilkinson's catalysts. Given these requirements, fluorous biphasic hydrosilylation catalysis was proved to be successful since [BMIm][B{C6H4—(SiMe2CH2CH2C6F13)-p}4] formed a homogenous system with the reactants and catalyst at elevated temperatures allowing the reaction to occur and upon cooling and phase separation, resulted in the recovery and subsequent recycling of the catalyst efficiently, even after 15 catalytic cycles. The reaction rate did not surpass the traditional method standards, however, the successful catalyst recovery clearly displayed a significant improvement exhibiting the potential for introducing fluorous biphasic ionic liquid systems for other types of catalysis.
Instead of applying phosphonium ionic liquids as solvents, the salts have been used for phase transfer catalysis, see reference (9). Phase transfer catalysis approach is used when the reactants are located in orthogonal phases. If one of the reactants is a poorly soluble salt the anion can be transported from one phase to the other by interaction with a lipophilic, bulky cation or crown ether, inducing the desired reaction to take place. Fluorinated phosphonium salts (8c) are excellent candidates for phase transfer catalysis since the perfluorinated substituents on the cation or anion are both lipophilic and hydrophobic and could therefore be used in either organic/aqueous, fluorous/organic or fluorous/aqueous biphasic mixtures.
The possibility of undergoing catalysis in fluorous solvents results in a large range of potential reactions to prepare various synthetic targets. Phosphonium salts [PR4][A] where R═(CH2)2(CF2)nCF3 where n=5, 7 and A=I, Br, have been applied as phase transfer catalysts for fluorous/aqueous biphasic halide substitution reactions and were recyclable for up to 4 runs.
Another separation technique that involves phosphonium ionic liquids includes using alkyl non-fluorinated phosphonium salts paired with fluorinated imides or phosphates as an extractant for the removal of proteins, protein fragments and/or peptides from biological samples, as disclosed in United States Patent Publication 2007/0026460 A1 (reference 16). The extraction procedure results in the removal of intact proteins that are not degraded and therefore can be thoroughly examined for the presence of disease.
There have been extensive studies on materials that have non-stick surfaces and thus are hydrophobic and oleophobic. Key components of these types of surfaces typically include geometric roughness on the micron to nanoscale and a low free energy coating, see reference (17). Either a rough surface can be prepared and subsequently coated with a hydrophobic substance, or a smooth low free energy material can be prepared and then patterned to generate a coarse surface morphology. The standard method for determining the degree of hydrophobicity of a material involves measuring the contact angle of a liquid droplet, such as water on the surface. If the contact angle is greater than 90° but less than 150° the surface is considered hydrophobic, while if the contact angle is greater than 150° the material is superhydrophobic. Moreover, with increased hydrophobicity, the non-stick properties of the material are superior.
Teflon, a common, commercially available non-stick coating or substance composed of a perfluorinated polymer, polytetrafluoroethylene (PTFE) has a contact angle of 107°. Generally the low free energy materials are perfluorinated molecules, such as Teflon, which with time and heat can release or degrade into toxic volatile compounds. Furthermore, the synthesis of some highly fluorinated polymers involves the generation of toxic volatile compounds such as perfluorocarboxylates (PFCAs), see reference (18).
Therefore a novel material that is superhydrophobic, non-volatile and thermally stable is required in order to improve the current technologies.